playschool vs play group

playschool and play group both are nouns.

Word	Noun	Adjective	Verb	Adverb
playschool	Yes	No	No	No
play group	Yes	No	No	No

As nouns, playschool and play group are synonyms defined as:

playschool and play group: a small informal nursery group meeting for half-day sessions

playschool (noun)	play group (noun)
a small informal nursery group meeting for half-day sessions	a small informal nursery group meeting for half-day sessions